1. Field of the Invention
The present invention relates to high temperature superconductor bearings that can produce strong levitation forces. This kind of bearings can be utilized to support rotating machinery with no mechanical contact, including flywheel energy storage systems which can convert electrical energy into kinetic energy of a rotating member and re-convert the kinetic energy into electrical energy.
2. Description of the Background Art
Bearings are an integral part for all rotating devices. In order to reduce the energy loss caused by the friction of the rotating members of the devices, ball bearings or journal bearings with fluid are used. In this case, since a force is exerted owing to the mechanical contact, there is a limitation in reducing the friction.
Therefore, non-contact bearings have been introduced which use permanent magnets and electromagnets. In these bearings, a rotating member is levitated by an attractive or repulsive force produced by the magnet or the electromagnet for thereby implementing a non-contact rotation. In this case, an active control is used in order to stabilize the axle. This technique requires an expensive circuit and control devices, and the energy is continuously consumed by the system during the use of the bearings.
Recently, high temperature superconductors (HTS) which become perfectly diamagnetic under certain conditions, i.e. which exclude magnetic field from it, have been discovered. Using these materials, non-contact bearings which do not require an active control have been disclosed taking advantage of the property that once the magnetic field has penetrated the material, it is retained and pinned inside the material.
FIG. 1 illustrates an example of the magnetic flux pinning which is achieved using a permanent magnet 11 and a high temperature superconductor 12.
As the magnetic field generated by the permanent magnet 11 is pinned inside the high temperature superconductor 12, the magnet 11 is held close to the HTS with an elastic force below the critical temperature where superconductivity takes place. Since the magnet 11 does not receive a kinetic resistance in the direction in which there is no variation of the magnetic flux density, it is possible to make a rotation with no mechanical friction.
FIGS. 2A through 2C illustrate the conventional thrust bearing. FIG. 2A shows a bottom view and a cross-sectional view illustrating a plurality of permanent magnets 21. In this construction, the problem that the rotor magnet can not be made of single permanent magnet is overcome. In the rotor 22, a plurality of permanent magnets 21 made of similar magnets having a predetermined characteristic are installed at a predetermined interval.
FIG. 2B illustrates the magnetic flux density distribution by the rotor 22 including the permanent magnet 21. As seen in the magnetic flux density curve 23, a nonuniform magnetic flux density is formed in the rotational direction. Even if a plurality of circular-arc-shaped rotors tied together are used instead of the cylindrical magnets, the nonuniformity of the magnetic flux density does exist due to defects in the material and due to demagnetization, thereby causing rotational losses.
FIG. 2C is a perspective view illustrating how the rotor 22 including a plurality of magnets 21 are held above the high temperature superconductor 12.
FIG. 3 is a view illustrating a high temperature superconductor journal bearing using a permanent magnet according to the prior art. As shown in FIG. 4, the rotor 32 may be formed of a plurality of cylindrical magnets 31 or a plurality of ring shaped magnets 35 and is installed in a tubular high temperature superconductor 33.
FIGS. 4A and 4B illustrate the configuration of the rotors which may be adapted for the conventional high temperature superconductor journal bearing. FIG. 4A illustrates a magnet arrangement in which magnetic poles of the cylindrical magnets 31 contact opposite poles of the magnets. FIG. 4B is a view illustrating the magnet arrangement in which the same poles of the ring shaped magnet 35 contact each other around the rotor shaft 34. The rotor shaft 34 is made of a non-magnetic material or a diamagnetic material.
As shown in FIG. 4B, in the construction in which the like poles face each other, the magnetic flux diverge radially outward between the poles of the magnets so that it is possible to obtain a strong force compared to the construction in which the opposite poles contact as shown in FIG. 4A. A high permeability material such as xcexc-metal or a ferromagnetic material is preferred to lower the magnetic reluctance.
In the conventional construction, the journal bearing rotor is constructed by arranging magnets like (N-S)/(N-S)/(N-S)/(N-S) as shown in FIG. 4A. In this case, however, the magnetic flux emerging from both ends of the rotor magnets only contribute to the magnetic force and it is impossible to effectively use the high temperature superconductor. Therefore, the ring shaped magnets 35 are stacked in opposing polarity, namely, in the configuration of (N-S)/(S-N)/(N-S)/(S-N) as shown in FIG. 4B, and the rotor shaft 34 is inserted into the hole.
In the case of the disc shaped thrust bearing as shown in FIG. 2C, the high temperature superconductor is inserted into the liquid nitrogen container, and the magnets are attached to the bottom of the rotor in such a manner that the pole surfaces of the magnets comprise the bottom surface of the rotor. Therefore, a force is generated between the rotor and the high temperature superconductor by the thusly generated magnetic field. In addition, in a thrust bearing, a superconductor magnet is placed lower as a stator instead of the high temperature superconductor, and then a high temperature superconductor is attached to the bottom of the rotor for thereby supporting the weight of the rotor. In this case, a predetermined shaped coil of superconductor film forms the superconductor magnet for thereby providing a straw hat-shaped magnetic density distribution, and then the high temperature superconductor of the rotor is inserted at the concave part.
In order to generate a strong magnetic force, a thrust bearing requires a strong magnet of large size. However, since it is difficult to fabricate a large size magnet having a uniform magnetization, a plurality of magnets are attached to the rotating plate. In this case, even when the magnets having the similar characteristics are attached, the nonuniformity of the magnetic flux density still exists due to defects in the material or due to the demagnetization, thereby causing a rotational loss.
In the prior art using a superconductor magnet for the stator, the magnetic flux density is uniformly formed in the rotational direction using the superconductor magnet, and there is an advantage in that it is possible to generate a very strong magnetic field compared to the regular magnets. However, in this case, diamagnetism in which the magnetic field is excluded from the superconductor is used, and it provides a stability only with the weight. When an asymmetrical magnetic flux pinning occurs in the high temperature superconductor attached to the rotor in the rotational direction, vibrational and rotational losses may occur.
In the case of the journal bearings, since a shaft is inserted at the center of the rotor magnet arrangement, the total volume of the magnets is reduced. When a strong force such as the weight, etc. is applied to the rotating member, the levitation force which is needed for the non-contact rotation of the rotating member is provided only based on the magnetic flux pinning of the high temperature superconductor and it is relatively weak.
In the case of the prior art thrust bearings, the rotational loss is large due to the nonuniformity of the magnetic flux density, and in the case of the journal bearings, it is very hard to obtain a strong levitation force.
It is an object of the present invention to provide high temperature superconductor bearings providing a strong levitation force and enabling development of horizontal-axle flywheel energy storage devices which overcome the aforementioned problems encountered in the prior art.
In the present invention, the non-contact journal bearing which levitates and supports the rotor using a predetermined interrelationship between a superconductor and a magnet is constructed as follows. A high temperature superconductor formed of high temperature superconductor film is used to make the rotor magnets. A plurality of magnets are stacked in opposing polarity as (N-S)/(S-N)/(N-S)/(S-N) with a predetermined gap between the opposing poles in a cylindrical container made of non-magnetic material, so that the magnetic field lines diverge out of the gaps mainly in the axial direction. The magnetic field of the rotor is fixed using a cylindrical stator made of one or a plurality of high temperature superconductor pieces for thereby preventing the escape of the rotating members and thus off-setting the force such as the weight, etc. using the magnetic pressure.
In the present invention, the magnets are installed opposite the outer circumferential surface of the cylindrical container of the stator made of high temperature superconductor, so that the attractive and repulsive forces applied to the rotor magnets are increased for thereby increasing the levitation force. In addition, the magnets are installed to be opposite at the upward and downward surfaces of the stator for thereby increasing the levitation force, and the pinning force is generated by the superconductor installed at the leftward and rightward surfaces of the rotor.
In the present invention, the horizontal-axle flywheel energy storage system is realized using the high temperature superconductor journal bearings as follows. A horizontal axle is used to support and lift the flywheel, thus having the rotational axle being perpendicular to the direction of its weight. One or a plurality of flywheels and a plurality of high temperature superconductor journal bearings are installed at the rotational axle, a non-contact motor/power generator is connected with the axle and is connected with a power conversion unit and a control unit installed outside the vacuum/safety container. In order to make a large capacity flywheel energy storage system, a plurality of flywheels and bearings are installed at the rotary axle for thereby increasing the rotational moment of inertia.
To achieve the above objects, there is provided a high temperature superconductor bearing generating a strong force and enabling the development of a horizontal axle flywheel energy storage system. It includes a journal formed of high temperature superconductor magnets made of high temperature superconductor film, and a semi-cylindrical stator formed of a plurality of high temperature superconductors installed opposite the high temperature superconductor magnet journal or the permanent magnet journal for thereby off-setting the force such as a weight applied to the rotor using a magnetic pressure.
To achieve the above objects, there is provided a horizontal axle flywheel energy storage system which includes a horizontal rotary axle, which supports the flywheel, and high temperature superconductor journal bearings installed at the horizontal axle for thereby supporting the weight of the rotating members.
Additional advantages, objects and features of the invention will become apparent from the description which follows.